# Novel Blood-Based Extracellular Vesicle-Derived Biomarkers in Small Cell Lung Cancer Identified via Proximity Extension Assay

## TL;DR

This study identifies blood-based biomarkers for early detection of small cell lung cancer using proteins from extracellular vesicles.

## Contribution

The study introduces novel extracellular vesicle-derived protein biomarkers for diagnosing small cell lung cancer.

## Key findings

- Five proteins showed strong discrimination between SCLC patients and healthy controls with AUCs of 0.95–0.98.
- A two-protein panel (LAP-TGF-β1 and PDGF-B) achieved an out-of-fold AUC of 0.96 for SCLC detection.
- NOS3, VEGFR-2, and ANGPT2 levels correlated with tumor reduction after chemotherapy.

## Abstract

Small cell lung cancer (SCLC) is a very aggressive lung tumor with high mortality and a late onset of symptoms. Detecting this disease is usually only possible at late stages, thus limiting treatment options. To date, there are no universally accepted biomarkers available that could aid in diagnosis. Therefore, the aim of this study was to detect changes in the expression levels of proteins carried by extracellular vesicles to pave the way for blood-based biomarkers for SCLC. Using a targeted protein analysis, it was possible to identify a specific pair of proteins that could distinguish healthy people from patients with SCLC. This study shows the potential of extracellular vesicle-derived proteins in the future diagnosis of SCLC.

Background: Small cell lung cancer (SCLC) is an aggressive malignancy with rapid progression and early metastasis, yet it lacks validated biomarkers for early diagnosis and treatment monitoring. Extracellular vesicles (EVs) are nano-sized particles released by cells that carry cargo reflective of their origin, making them promising candidates for liquid biopsy-based biomarker discovery. Methods: Plasma-derived EVs were isolated from 29 SCLC patients and 28 healthy controls (HCs) using ultracentrifugation and characterized via nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM). Proteomic profiling was performed using the Olink® Immuno-Oncology panel. Group differences were analyzed using multivariate models (Boruta, Elastic Net, and partial least squares discriminant analysis). Diagnostic potential was assessed using ROC analysis, and predictive response associations were evaluated by correlating EV protein changes with tumor size reduction (FDR-adjusted Spearman). Results: Of the 58 detected proteins, 36 were significantly upregulated in SCLC. PDGF-B, CXCL5, CCL17, EGF, and LAP-TGF-β1 showed good discriminatory performance (AUC 0.95–0.98). Additionally, a two-protein panel (LAP-TGF-β1 and PDGF-B) achieved an out-of-fold AUC of 0.96 (CI 0.89–1.00). NOS3, VEGFR-2, and ANGPT2 levels correlated inversely with tumor reduction after chemotherapy. Conclusions: These exploratory findings highlight EV proteomics as a minimally invasive platform for potential SCLC diagnosis and monitoring.